When Abram was ninety-nine years old the Lord appeared to Abram and said to him, “I am God Almighty;[a] walk before me, and be blameless, 2 that I may make my covenant between me and you, and may multiply you greatly.” 3 Then Abram fell on his face. And God said to him, 4 “Behold, my covenant is with you, and you shall be the father of a multitude of nations.
Genesis 17:1-4

Have you ever thought of yourself as part of a fulfillment of God’s promise to Abraham?  Not a topic of conversation at the water cooler lately? Maybe it should be. If you have faith in Jesus Christ as your Salvation, you are the living fulfillment of God’s promise.

7 Know then that it is those of faith who are the sons of Abraham. 8 And the Scripture, foreseeing that God would justify[c] the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “In you shall all the nations be blessed.” 9 So then, those who are of faith are blessed along with Abraham, the man of faith. Galatians 3:7-9

It can get pretty easy sometimes to build a case for or against yourself to God.  You put more money in the offering plate or you don’t; you remember to pray for a missionary or you scroll through social media; you share the Gospel with your neighbor, or you close the garage door as fast you can.  You either begin to pat yourself on the back or condemn yourself to Hell.  Like God is going to judge your eternity based on those things.

That was the problem people were having back when Paul wrote his letter to the Galatians.  They were getting caught up in circumcision (among other things) because God had commanded circumcision of Abraham and his offspring as part of His promise.  

9 And God said to Abraham, “As for you, you shall keep my covenant, you and your offspring after you throughout their generations. 10 This is my covenant, which you shall keep, between me and you and your offspring after you: Every male among you shall be circumcised. 11 You shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between me and you.
Genesis 17:9-11

Abraham made an agreement with God and it had been followed faithfully by the children of Abraham.  They set themselves apart through this physical act. And so the law began, and man began to learn the heart of God for humanity.

But the act of circumcision was not God’s promise.  The act of Salvation through God was God’s promise.  All humanity had to do was trust God with that promise.  It was Abraham’s faith that God called righteousness.  His faith.  Not his actions. Though his actions were an outward sign of his faith.  But if he had relied on his own actions, he would never have had any faith, and never been counted as righteous by God.

10 For all who rely on works of the law are under a curse; for it is written, “Cursed be everyone who does not abide by all things written in the Book of the Law, and do them.” 11 Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.”

Galatians 3:10-11

The only physical act that could count to us as righteousness was something only God could fulfill: the death, burial and resurrection of Jesus.  Jesus’s perfect act of obedience was faithful to the Law and fulfilled the Law. In this act He offered all of humanity full reconciliation with God through faith and the “circumcision of the heart” that comes from that faith.

12 But the law is not of faith, rather “The one who does them shall live by them.” 13 Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, “Cursed is everyone who is hanged on a tree”— 14 so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit[e] through faith.

Galatians 3:12-14

Christ did what we could not.  Christ gave what we could not earn.  Only faith in Jesus as the fulfillment of God’s promise to Abraham gives us the eternal life and inheritance that we long for and were promised.

19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary. 20 Now an intermediary implies more than one, but God is one.
21 Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. 22 But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe.

Galatians 3:19-22

The law was a type of placeholder for Jesus. The law came to give us a way to show obedience to God through faith in what God had given.  But the law couldn’t give life. It could only give death (through disobedience).  

Faith in Christ, however, brings life.

23 Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. 24 So then, the law was our guardian until Christ came, in order that we might be justified by faith. 25 But now that faith has come, we are no longer under a guardian, 26 for in Christ Jesus you are all sons of God, through faith. 27 For as many of you as were baptized into Christ have put on Christ. 28 There is neither Jew nor Greek, there is neither slave[g] nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ’s, then you are Abraham’s offspring, heirs according to promise.
Galatians 3:23-29

There you go.  If you have faith in Christ as your Savior, you are a living, breathing, heart-circumcised, testimony of God’s faithfulness to His promise. You are a child of promise.